Non-consumable electrode vacuum arc furnaces for steel,zirconium,titanium and other metals and processes for working said metals



United States Patent lnventor Appl. No.

Filed Patented Assignee NON-CONSUMABLE ELECTRODE VACUUM ARC FURNACES FORSTEEL, ZIRCONIUM, TITANIUM AND OTHER METALS AND PROCESSES FOR [50] Fieldof Search 219/210, 390; 266/34(V); 3 l 5/] l; 310/89, 9; 75/10l4, 49;l3/3l, 9

[56] References Cited UNITED STATES PATENTS 2,871,533 2/1959 Swainsonl3/9UX 3,370,119 2/1968 Grimm et al l3/9X Primary ExaminerBernard A.Gilheany Assistant Examiner-Roy N. Envall, Jr. Attorneys-Ar T. Stratton,C. L. McHale and M. I. Hull ABSTRACT: Vacuum furnace apparatus employingone or WORKING SAID M A more nonconsumable electrodes and controlledmaterial feed Clams 12 Drawmg at one or more locations; coordinatedmaterial feed and ingot U.S.Cl 13/31, movement which provides forcontinuous casting; and new 75/10, 75/49, 266/34 and improved feedingmechanism including separate material Int. Cl HOSb 7/18 feed hopperswhere alloys are being cast.

' COOLING WATER I I34 col ae FIELD L '28 Eiiiifi H HOPPER HOPPER A) if ii I39 V 146 a 3 V I v I 1 l l\\\ Q l i l .,|31 P s I I53 .-l38 t: I d-22I24 i I I26 I L T z Q 3 I25 I30 I52 149 R sum 1 OF 4 3546348 PATENTEUBEE-8 I976 PRIOR ART 3 PHASE SOURCE PATENTEDUEC-BIQIB 3546' 348 SHEET 2OF 4 COOLING WATER MAIN POWER DC FIELD COIL I-NVENTOR Serofino M.DeCorso ATTORNEY PATENTED BC8 I970 SHEET 3 OF 4 COOLING WATER s HOPPERFEED CHARGE PARTICULATE CHARGE FEED HOPPER I34 I DC FIELD COlL A FIG];

144 HOPPER PTO VACUUM PUMP m/ mm w W R p, mm u P m \m f: g I83 r-FEEDCHARGE SHEET 0F 4 ALTERNATE i/FEED CHARGE NON-CONSUMABLE ELECTRODEVACUUM ARC FURNACES FOR STEEL, ZIRCONIUM, TITANIUM AND OTHER METALS ANDPROCESSES FOR WORKING SAID METALS CROSS REFERENCE TO RELATEDAPPLICATIONS This application is related to application Ser. No. 407,332filed Oct. 29, 1964, now abandoned, by A. M. Bruning for ElectricArc'Furnace and Non-Consumable Electrode Suitable for Use Thereim Ser.No. 484,799 filed Oct. 6, 1966, now U.S. Pat; No. 3,381,540, by S. M.DeCorso et al. for Process for Iron Ore Reduction and :ElectricFumace'for Iron Ore Reduction Having at Least .One Non-ConsumableElectrode; application Ser. No. 584,798, filed Oct. 6, 1966 by A. M.Bruning et al. for "Electrode Heated-Oxygen Steel Furnace and Processfor Producing Steek an application of S. M. DeCorso et al. forSmall'Diameter Fluid Cooled Arc-Rotating Electrode; Ser. No. 663,714,filed Aug. 28, 1967, now U.S. Pat. No. 3,377,4l8; and Ser. No. 554,427,filed June l, [966 by S. M. DeCorso et al. for Copper Ore Reduction andMetal Refining Process and Apparatus for Use Therein, all of theabove-identifiedcopending applications being assigned to the assignee ofthe instant invention.

BACKGROUND OF THE lNVENTlON l. Field of the Invention a The inventionrelates to apparatus and processes for obtaining, treating and workingmetals in a vacuum including steel, tungsten, molybdenum, tantalum,columbium, zirconium, titanium and others.

' 2. Description of the Prior Art Some of the apparatus and processesdescribed and claimed herein relate to improvements in the -H process,well known in the art and described in the literature of the artincluding an article entitled The D-H Vacuum Process For Molten Steel"by P. J. Wooding and W. Sieckman, Transactions of the Vacuum MetallurgyConference, 1960, pp. 243-252. One of the disadvantages of the prior artD-H process results from the fact that the steel tends to cool as it isbeing degassed and present techniques involve preheating of the vacuumvessel and heat addition by resistance heating within the vacuum vessel.l overcome these disadvantages by providing a nonconsumable electrode orelectrodes within the vacuum vessel to supply heat to the moltenmaterial in the vacuum vessel during the degassing operation whichrenders unnecessary separate preheating of the vacuum'vessel, rendersunnecessary superheating of steel before the process is begun, providesfor an increased steel movement rate' (degassing rate), and permits aprolonged spraying time .to produce better steel.

In other embodiments of vacuum furnace apparatus according to myinvention, and which may be used in practicing the processes of myinvention, 1 overcome many limitations and disadvantages of prior artfurnace processes and apparatus. For example, in conventional vacuumfurnace operation it must be feasible to form the material to be chargedinto an electrode shape; the forming ofelectrodes from certainrefractory metals is difficult and costly, in some cases requiringcompacting at half pressures and requiring welding some gas or impurityis brought into the furnace within the electrode, making it difficult tokeep impurity levels of the formed electrode low; the power input andvoltage current characteristics of the arc in prior art furnaces isusually a function of the material and method of forming the electrode,and the power input to the furnace cannot be varied independently ofelectrode consumption; consumable electrode operation is almostinvariably direct current and wide variation occurs in the alloca' tionsof heating betweenelectrode and ingot, depending upon the metals to bemelted. It has been found in practice that some metals heat up morewhile'acting as anodes while other metals heat up more while actingas-cathodes; occasional instability occurs leading to arcing to themold, which structure cannot withstand the resulting heating; materialsof poor electrical conductivity such as boron and silicon presentdifficulties for consumable electrode operation and require preheatingbefore suitable current flow may be established.

1 overcome these disadvantages by a number of unique and novel features;I provide a nonconsumable electrode or electrodes in which the arcis.caused to move over the electrode face by action of a magneticfieldgenerated for this purpose about the electrode face. This broad ideaconstitutes no part of the instant invention, having been described andclaimed in the aforementioned copending application of A. M. Bruning,and further described and claimed in a copending application of S. M.DeCorso et al. for Non-Consumable Arc Electrode," Ser. No. 407,327,filed Oct. 29, 1964, now U.S. Pat. No. 3,398,229.

I provide material feed in the form of powder, pellets, wire or rod. Inthe case of wire or red feed, the main arcing capability remains withthe electrode face, so that arcing performance does not depend on thematerials surface or current conducting properties; thus the feedingmethod is concerned primarily with getting material to the arcing zone,and the material being fed does not play any primary role in the arcingaction. Feeding action may be continuous or intermittent. In one or moreembodiments I use a lock hopper where particulate material is fed.

1 provide controlled arc movement to provide stabilization and permitoperation on either alternating current or direct current power.Furthermore, the magnetic flux set up by the electrode field coil reactswith the current path to cause stirring of the melt. The stirring. isvery important for improved refining in particular in large ingotorfurnace sizes.

l provide controlled material feed location to assist arc stabilizationand/or to provide radiation shielding between arc and walls of the mold.My app'aratus and processes employ coordinated material feed andingotmovement to provide for continuous casting, which will reduce losses atingot'ends or skulls and reduce down time losses for installingelectrodes and removing ingots.

The nonconsumable electrode design which I employ is such that thematerial being melted splashes oris transported to the electrode face,forming a coating thereon which serves as thermal insulation and servesto protect the electrode face from arc action. This has been observed inpractice on electrodes employed in utilizing my invention.

l employ as an electrode face material copper or copper with refractorymetal coatings and other metals having similar characteristics.

My feeding mechanism or mechanisms may include the use .of inert gas totransport aparticulate charge to the arc site.

' While alloys are being cast the desired composition may be attained byuse of separate material feed hoppers, or by using a single hopper withthe charge well mixed. In either case the alloy composition may bereadily altered from one casting to the next, a change not readilyaccomplished when the alloy must be formed into a consumable electrode.

Summarizing the many advantages which accrue from the apparatus andprocesses of my invention: the necessity and expense of forming anelectrode of the material to be charged is obviated; power input may bemade relatively independent of charged material thereby providing morepredictable heating of the ingot surface than is now obtainable withconsumable electrodes; a feature which reduces the cost of design andinstallation of power supplies for each furnace by substantiallyremoving a variable which can be unpredictable, namely the bulk andsurface electrical properties of the consumable electrode; continuouscasting is possible where the charge feed rate and ingot movement arecoordinated as they may be in the apparatus and processes of myinvention, thus reducing.

the cost of handling and placing the consumable electrodes, and reducingingot end losses;-improved purity may be obtained due to reducedimpurity levels possible in a particular charge and secondly due to theability to do extended refining by operating at low charge feed rates inrelation to power input; arc casting of materials which are not goodelectrical conductors is facilitated by the use of the nonconsumableelectrode since the charge material need not carry current until it isin the heated state in the ingot; are stabilization is obtained by thelocation of the charge feed since the charge feed stream presents a lowimpedance path for the arc; in alternating current operation, ascompared to present direct current operation, the cost of rectifiers issaved because for large furnaces three phase operation is possible bythe use of three electrodes; by using a nonconsumable electrodestructure which is hollow in cross section, additional gas flow area isavailable along the axis of electrode-mold and consequently lowerpressures are obtainable at the arc site and this in turn increases thepurity level of the ingots; gas addition at the electrode site toinfluence arc behavior is easily accomplished by my nonconsumableelectrode and this is true also for gas addition for the purpose ofchemical reaction with the metal charge or impurities in the charge.

For simplicity of illustration I have shown apparatus illustrating myinvention and suitable for practicing the processes of my invention insimple form; my invention includes the use of all additional metalhandling and metal processing apparatus of conventional design now wellknown in the art.

BRIEF DESCRIPTION OF THE DRAWINGS consumable electrodes have an arctherebetween for supplying heat to the molten material.

FIG. 4 illustrates in plan view the top of a vacuum vessel having threenonconsumable electrodes arranged in a triangular pattern for supplyingheat to the material in the vacuum vessel during the degassingoperation, the three electrodes being connected to the three phases of athree-phase source. Such an electrode arrangement may also be used wherean ingot is to be formed.

FIG. 5 shows an improved vacuum vessel suitable for practicing animproved process in which two concentric nonconsumable electrodesproduce two arcs to the molten metal in the vacuum'vessel, or an arebetween electrodes.

FIG. 6 is a plan view ofa vacuum vessel in which three concentricelectrodes are employed, the three electrodes being connected tothethree phases of a three-phase source. Such an electrode arrangement mayalso be used where an ingot is to be formed.

FIG. 7 shows a nonconsumable electrode for producing an ingot in, a moldwith a plurality of hopper means for feeding particulate material to themelt, down the side of the mold, through a central aperture in theelectrode, and in the'space between the electrode and a cylindricalsleeve surrounding the electrode.

FIG. 8 shows a mold employing nonconsumable electrodes for continuouscasting.

FIG. 9 shows apparatus for forming an ingot in a mold in which feedmaterial is fed to the melt through a central axially extendingpassageway in the electrode or electrodes.

FIG. I0 shows a mold for forming an ingot in which two coaxiallydisposed nonconsumable electrodes are employed for producing an arewhich melts the material in the mold.

FIG. I1 shows a skull furnace according to my invention which may beemployed for forming a single ingot, with alternate means of feedingcharge to the skull furnace.

FIG. 12 is a diagrammatic view illustrating how the magnetic field inthe nonconsumable electrode which I employ assists in stirring the melt.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Particular reference is madenow to FIG. I which shows apparatus for practicing the aforementionedD-H process according to the prior art. For simplicity of illustrationthe v vacuum treatmentvessel and the ladle are shown as being formed ofmetal but it will be understood'that'in practice both of these are linedwith refractory material or are fluid cooled.

The treatment vessel is generally designated 21 and the ladle isgenerally designated 22 Nozzle 24 of the treatment vessel extends intothe melt 23 and a portion of themelt is shown as having been sucked intothetre atment vessel 21 as a result of partially evacuating the vesselthrough conduit 25jcohnee ted to vacuum pump 26. When theichamber 27 'ofthe'yaeuurn vessel 21 is evacuated, the pressure of the nqpsgfi redifthe uppersurface 28 of the melt23tforces the molten nietal up throughthe nozzle into the treatmentvessel. Molten material 23 may be referredto in the claims as a volume of materialfto be treated. Cyclic variationof the emersion depth of th'esuE-Q tion nozzle forces successiveportions of the melt, which may be steel or some other metal which it isdesired to purify, into the evacuated chamber where it is degassed, theimpurities therein having vapor pressures which are'less than the vaporpressure of the material of the melt, the volatilized impurities beingremovedby the vacuum pump 26. Pump 26 may run continuouslyintermittently, or chamber 27 may be evacuated before the process isbegun. For a fuller understanding of the' prior art D-H process,reference may be had to the aforementioned article by WoodingandSieckr'nan.

One of the fundamental requirements for effective gas removal is a largesurface area exposed to the vacuum, and unfortunately this is also thebest possible way to lose tempera- I ture very quickly. Accordingly,prior an apparatus requires some effectivefmeans for preventingradiation lossfrom-the' metal. Thisis accomplished by heating the vesselto thetein-j perature of the molten steel. Prior art apparatus employsresistive heating for the vacuum vessel. Additional requirements I arethat the bath must beshallow' with as large as possible a surface area,and a space must be provided'for the violent turbulence which. occursduring treatment. Oxygen, hydrogen and nitrogen may be removed from themelt in the vacuum vessel, hydrogen and oxygen sampling beingaccomplished by the well known immersion mold method and analysis byvacuum fusion. Also chemical determination of the oxygen content may beemployed. I

Particular reference is made now toFIG. 2 where myim;

proved apparatus for practicing my improved D-H process is shown. Ladle32 is seen ashaving a refractory inner'lining 33 i and an outer shell ofmetal 34. The vacuum or treatment ves sel generally designated 36 has arefractory inner lining 37, an outer shell of metal 38, and a nozzle 39extending into 'the melt 40, the nozzle 39 not only having a refractorylining on the inside thereof but having a refractory lining portion 41on the outside thereof. It will 'be understood that means, not shown forconvenience of illustration, is provided for adjusting the position ofthe nozzle vertically so that various portions of the melt may be suckedup into thevacuumvessel or'forced up into the vacuum vessel as a resultof atmosphericpressure on the upper surface of the melt.

Conduit 49 connects vacuum 'pump 50 to the interior chamber 51 of thevacuum vesseL'Pump 50 may runcontinuously, intermittently, or chamber 51maybe evacuated before the process begun.

Cover 44 for the vacuum vessel has a portion 45 composed of insulatingmaterial with a bore 46-therein through which ing means has a magneticfield producing coil"56fldisposed therein which sets up a magnetic fieldwhich causesthe arc58 to move substantially continuously around theannular arcing surface 53. Arc 58 is shown as being a multiple are ordiffused are as frequently occurs in practice. The electrode is seentohave a central passageway 59 which may extend through the entireelectrode if desired, the upper and being closed by means, not shown forconvenience of illustration, to prevent the loss of heat therefrom.Leads 61 and 62 bring current for energizing the aforementioned fieldcoil 56; lead 63 is connected to one terminal of a source of potentialwhich produces the arc 58. It is understood that the supporting columnportion of the electrode includes conductive means extending from thelead 63 to the metallic arcing surface 53 to complete a current path.Conduits 65 and 66 pass through passageways in the electrode, not shownfor convenience of illustration, and communicate with the aforementionedpassageway or passageways 54 in the electrode tip for bringing coolingfluid to the tip and conducting fluid therefrom. The nonconsumableelectrode itself forms no part of the instant invention; suitablenonconsumable electrodes are described in several copending patentapplications assigned to the assignee of the instant invention includingan application for Non-Consumable Arc Electrode by S. M. DeCorso et al.Ser. No. 407,327, filed Oct. 29, 1964, and application for Electrode" byS. M. DeCorso, Ser. No. 479,965, filed Aug. 16, I965, now US. Pat. No.3,369,067. r

In order to complete an electric circuit to the melt 67 the refractorylining 37 is seen as having a gap or hole 68 therein adjacent a portionof the metal shell 69 which is insulated from the remainder of the metalshell by encircling insulating means 70. Wall portion 69 is fluid cooledas by fluid flow passageway 72 connected to suitable fluid inlet andoutlet means, not shown for convenience of illustration, and wallportion 69 has lead 71 connected thereto, lead 71 being connected by wayof rheostat 74 to the terminal of opposite polarity of the source ofpotential which produces the arc 58. The melt 69 passes through the hole68 and makes electrical contact with metallic wall portion 69 completinga current v path.

Where leads 63 and 71 are connected to a source of direct current toproduce the arc 58, preferably the electrode 47 is the anode, because ithas been found in practicethat an electrode connected to form the anodeof adirect current circuit undergoes less wear than a similar electrodeconnected to form the cathode.

means is provided for adjusting the current which produces the arc 58,symbolized by rheostat 74 in lead 71.

My invention obviates-the necessity for separate preheating of thevacuum vessel required in the prior art D-H process as previouslyexplained. By adjusting the amount of heat supplied to the melt 67 Imaintain the melt at any desired temperature most effective for thedesired degassing operation. Furthermore, no super heating of the steelor other liquid or molten metal is necessary; superheating to providefor loss of heat in the vacuum vessel results-in an unnecessary andwasteful expenditure of electrical power. Furthermore, by adjusting thepower of the arc and the time that the arc takes place, the steelmovement rate, that is, the degassing rate may be increased, as willreadily be apparent, because I can quickly adjust the temperature ofthat portion of the melt within the vacuum vessel to provide for anoptimum degassing rate. Furthermore, since because of the are which Isupply to the molten metal in the vacuum'vessel, there is no substantialloss of heat therefrom, the spraying time that any particular portion ofthe metal is in the vacuum chamber may be prolonged produces bettersteel, purer metals, etc.

Reference is made now to FIG. 3, where for simplicity of illustrationonly the vacuum vessel is shown. For simplicity of illustration thevacuum vessel is shown as having walls of metal but it will beunderstood that the walls are fluid cooled or that there is a refractorylining similar to the refractory lining of FIG. 2 covering the entireinside including the inside of the nozzle and also the outside of thenozzle. In FIG. 3, the vacuum vessel 77 has oppositely disposed wallportions 78 and 79 composed of insulating. material through which passtwo nonconsumable electrodes generally designated 80 and 81, which it isunderstood are connected to terminals of opposite polarity of a sourceof potential, not shown for convenience of illustration, to produce theare 82. The are 82 supplies the necessary heat to the molten material inthe vacuum chamber, the arc current being adjustable. FIG. 3 has theadvantage that it is not necessary to form an electrical connection tothe molten steel or other molten steel metal material in the vacuumchamber.

Particular reference is made now to FIG. 4 where a plan view of a vacuumvessel generally designated 85 is shown having an insulating portion 92in the top cover thereof through which pass three nonconsumableelectrodes generally designated 86, 87 and 88, which it is understoodextend toward the molten liquid in the vacuum vessel and produce arcsthereto, the electrodes being connected by leads 89, 90 and 91respectively to a three-phase source of alternating current potential.By utilizing three electrodes connected to a three-phase sourceeconomies in power consumed may be effected as well as increasing theheating capacity which may be supplied to the molten material in thevacuum vessel.

Particular reference is made now to FIG. 5; vacuum vessel 95 has avacuum pump 96 connected thereto and has in the cover thereof aninsulating portion 97 through which pass two nonconsumable electrodescoaxially mounted with respect to each other, the electrodesbeingdesignated 98 and 99 and spaced from each other by annular spacermembers 100 and 101. Leads 102, 103 and 104 electrically connect the twoelectrodes and the melt respectively to a source of potential forproducing arcs 105 and 106 from the electrodes to the molten metal.Electrode 98 may be similar to electrode 47 described in connection withFIG. 2; electrode 99 is seen to have fluid flow passageway orpassageways 107 for conducting face. It will be understood that means,not shown for convenience of illustration, is provided forsimultaneously raising and lowering the electrodes 98 and 99.as thelevel of molten material in the vacuum chamber changes, and also toprovide the desired arc length, and that-means, not shown forconvenience of illustration, is provided for individually adjusting thepowers of the arcs 105 and 106.

Likewise it will be understood that means is provided for raising andlowering the electrodes 86, 87 and 88, FIG. 4.

Particular reference is made now to FIG. 6 where three concentricelectrodes 111, 112 and 113 are seen mounted in the cover 114 ofa vacuumchamber, connected by leads 115, 116 and 117 respectively to athreephase source of potential and separated from each other by annularinsulating members 118, 119 and 120 and also from the metallic portionof the cover.

Further, with respect to all of the embodiments of FIGS. 2 through 6inclusive, it will be'understood that the material in the ladle may be atap from an electric furnace or it could have come from a basic oxygenfurnace. After the molten material is purified by the degassingoperation to the desired state of purity as ascertained by many testswell known in the art, the ladle may be lowered and removed to a desiredoperating position where ingots may be poured from the purified moltenmetal. As previously stated, the vacuum vessel is preferably lined withrefractory material or fluid cooled by fluid passageways in the wallthereof.

As previously stated the embodiments described hereinbefore which employtwo or more electrodes offer the advantage of not having to makeelectrical connection to the molten metal, and as previously stated theyobviate the necessity for making the electrode the anode where a directcurrent is employed, it having been found in practice that when anelectrode forms the anode it is subject to less wear than when it isconnected to form the cathode of the circuit.

The embodiments of FIGS. 2 through 6 inclusive can be used to purify anymetal containing impurities having vapor pressures which would beremoved by the process.

Particular reference is made now to FIG. 7 which shows apparatus forproducing an ingot in a mold. FIG. 7 will be described with reference tothe use of the metal titanium to produce an ingot therefrom, but it willbe understood that it can be used to produce metals which are treated invacuum furnaces, these including tungsten, molybdenum, tantalum,columbium, zirconium, as well as titanium and other rare metals. In FIG.7 the mold is generally designated 123 and is shown in upper and lowerdetachable sections 124 and 125, the lower section being fluid cooled bypassageway 126; the mold generally designated 123 has a detachable base,not shown for convenience of illustration, but which may be constructedaccording to well known prior art practices; after the ingot is formedand allowed to cool it shrinks an appreciable distance from the wall ofthe mold, for example a quarter of an inch around the periphery of theingot, and thereafter the sections of the mold are disconnected, thebase is removed, and the ingot slipped from the mold in accordance withconventional practice.

For general information regarding the production, extractive metallurgy,and processing and fabrication of titanium, reference may be had to awork entitled Rare Metals Handbook Second Edition, edited by Hampel,Reinhold Publishing Corp. 1961, pages 559'579 inc. On page 561 of thatwork there is shown a simplified flow sheet for the extraction andrefining of titanium, and one stage includes the production of massivesponge titaniumwhich is crushed to provide particulate matter forfeeding to a vacuum furnace for producing an ingot. FIG. 7 shows ahopper 128 containing particulate titanium sponge. A nonconsumableelectrode generally designated 129 has a fluid passageway 130 forconducting heat flux from the arcing surface 131 and an axiallyextending passageway 132 therethrough communicating by way of conduit133 and valve 134 with an additional hopper 135 so that particulatecharge may be fed to the molten liquid through the axial passagewaythrough the electrode. Surrounding the electrode and spaced therefrom isa cylindrical jacket 137 forming an annular cylindrical passageway 138which communicates by conduit 139 and valve 140 with the aforementionedhopper 128 so that particulate matter may be fed to the molten pool 142through the annular passageway between the jacket and the electrode.

A still further hopper 144 is provided connected by valve 145 andconduit 146 to introduce particulate charge feed around the wall of themold. Lead 148 symbolizes means for connecting the electrode to oneterminal of a source of potential to produce the are 149, the moltenpool forming the surface of opposite polarity and being connected to theother terminal of the source ofpotential through the mold and/or ingotand lead 150. The portion of the ingot designated 151 designates therelatively cooled and hardened portion. The molten pool is designated152. The chamber within the mold is designated 153 and is evacuated byvacuum pump 154 connected to the chamber by conduit 155. I

As will be readily understood, as particulate matter is added to themolten pool, the level of the pool gradually rises within the mold, sothat the electrode is gradually withdrawn upward as the height of theingot increases.

In accordance with certain specifications and usages in the titaniumindustry, it is sometimes required that the ingot be remelted a secondtime to further reduce the amount of impurities therein and to provideimproved homogeneity in the ingot. It is usual to employ the ingotitself as an electrode in the second remelting operation, that is, as aconsumable electrode which is consumed during the process. On the otherhand it is usual to employ a nonconsumable electrode in the first ingotforming operation where the ingot is formed in a mold in a mannerheretofore described. The nonconsumable electrode of my invention offersmany advantages over the use of a graphite electrode employed as anonconsumable electrode. Generally a graphite electrode must be operatedunder limited and carefully controlled conditions to keep itsubstantially nonconsumable during the ingot-forming process. One ofthese undesirable conditions is that a graphite electrode must be kept acertain minimum distance from the melt, or the melt splashes on theelectrode, erodes graphite from the electrode and takes the graphiteback into the melt with it, forming titanium carbide, an undesiredimpurity. Furthermore, where a graphite electrode is employed as thenonconsumable elec- 600 F. to 800 F., representing heat flux removal atthe fate- 4X10 B.t.u./hr./ft. for a certain thickness range of thecopper arcing surface. At this temperature of 800 F. the vapor pres sureof copper is less than l0 atmospheres. It will be readily seen that amold having a nonconsumable electrode with a copper arcing surface canbe evacuated well below 20 mmsfof pressure, the lower limit for agraphite electrode, thereby in- I creasing greatly the rate of impurityremoval, so that removed impurities do not recondense within the moldand fall back" into the melt. Assuming a temperature of 3000 F. forthemelt, one which might be reached in practice, a mold having anonconsumable copper electrode can be evacuated to a level which wouldresult in the removal of certain impurities which would not be removedat all at 20 mms. of pressure, the vapor pressure or partial pressure ofthe impurity being belowQQ mm. at 3000 F. i

The apparatus of FIG. 7 also has the one polarity advantage heretoforementioned in that when the electrode is operated as an anode the usefullife thereof is prolonged. i

When the ingot 151' has reached the desired length, the

power to the arc is shut off, allowing the ingot time to cool, the mold'dismantled and the base removed, and the ingot slipped therefrom eitherfor further processing by remelting as aforedescribed or for otherprocessing.

Particular reference is madenow to FIG. 8 which shows an embodiment ofmy invention for continuous casting; as the.

ingot forms, the rigid part is gradually moved into thevacuiim;enclosure. It is seen that the mold generally designated'15 8-, FIG. 8,has a wall portion 157 and a retractable bottom- 159, which movesaxially with respect to the wall of the mold and has retracting ormoving means 160 secured thereto. Mean s- 160 may be slidable in a boreor opening in a removable base of the mold 158, the removable base notbeing shown for convenience of illustration, and being provided so thatthe ingot 161 may be removed from the mold, or if desired the member 159may provide the bottom of the mold, and when the member 159 reaches thelower end of wall portion 157. of the" mold as a result of theelongation of the ingot 161, the ingot may be removed therefrom. Ingot161 is shown as havinga molten pool 162 with charge material, 163 beingadded thereto? through the charging means 164 located in the top of themold, it being understood that the charging means 164 may beconnected tohopper means, not shown for convenience of illustration. The material inthe molten pool 162 is reduced toits molten state by heat from are 165shown as taking place. between two electrodes 166 and 167, passingthrough the: sidewalls of the mold and being insulated therefrom byinsulat ing members 168 and 169 respectively. Chamber 170: is. evacuatedby a pump 171 connected thereto by conduit: means 172.

It will be understood that in acontinuous castingprocess. utilizing theapparatus of FIG. 8, the charge feed rate and ingot movement arecoordinated, thus reducing the cost of? handling and placing consumableelectrodes, and also reducing ingot end losses.

It will be understood that the mold 158 may be fluid cooled if desiredor contain an inner lining or refractory materiaFif evacuated to a muchlower lev e l t han would be possible where it was desired to operate agraphite electrode, as a nonconsumable electrode, so that the chambermay be evacuated to a point limited only by the basic materials of themolten pool 162 with the result that impurities having vaporizingpressures above this pressure level-are removed by the vacuum pump 171.

Particular reference is made now to FIG. 9 where a mold 175, which maybe cooled by fluid means not shown, and which may include an inner wallof refractory material, not shown, has two electrodes 176 and 177passing through insulating portions 178 and 179 respectively in thesidewalls of the mold and having an are 180 therebetween. As seen, oneof the electrodes, 176, has an axial passageway 181 extendingtherethrough through which material 182 is fed to the molten poolportion 183 of ingot 184. The chamber 185 of mold 175 is connected byconduit means 186 to a vacuum pump, not shown for convenience ofillustration. Mold 175 is shown as having a detachable base 187 and ashaving therearound a field coil for setting up a magnetic field to stirthe melt, such a practice being well known in the prior art, the fieldcoil being designated 188.

It will be understood that both of the electrodes may have axialpassageways therethrough through which material may be fed to the moltenpool within the mold.

Particular reference is made now to FIG. where mold 222 has extendingthereinto two coaxially disposed electrodes generally designated 195 and196 electrically insulated from each other passing through insulation197 in the upper wall or top of the mold and having an are 198 producetherebetween. Electrode 195 may be similar to those previouslydescribed, having axial passageway 199 therethrough which is connectedby conduit 200 to a vacuum pump 201 for evacuating the chamber 202 byway of the central passageway through electrode 195. Electrode 196 isseen-as including, if desired, four generally coaxial cylindrical wallportions 211, 212, 213 and 214 forming a fluid passageway 215 forbringing cooling fluid .to and from the arcing surface and having thefield coil 216 therein which is energized to set up a force to rotatethe aforementioned are 198. Electrodes 195 and 196 may be maintained inspaced position with respect to each other by support member 217providing a cylindrical passageway 218 through which feed material 219is fed to molten pool 220 of the ingot 221 disposed in mold 222. Theaforementioned cylindrical passageway 218 between electrodes may .beconnected by conduit means 223 to a hopper, not shown for convenience ofillustration, for containing the feed material. It will be understoodthat the feed material may be fed through the passageway 218 at a numberof peripherally disposed paths therein, or feed material may be fedthroughout substantially the entire annular passageway, suitable conduitmeans 223 being provided for connecting the passageway to the feedhopper.

Particular reference is made now to FIG. 11 showing other apparatusembodying my invention for practicing processes of metal treatmentaccording to my invention. A skull furnace is generally designated 226and disposed within chamber-forming means 227. A vacuum chamber 228formed therein is evacuated by pump 229. Furnace 226 is seen to have apouring spout 230 and a ladle 231 both enclosed within the vacuumchamber, and the material in the furnace 226 is reduced to a moltencondition by an arc thereto from nonconsumable electrode 232 which maybe similar to nonconsumable electrode hereinbefore described having anaxially extending central passageway 233 which may be used for feedingmaterial into the furnace 226, it being understood that the electrode232 includes means for closing the upper end of the passagewaytherethrough to insure that the vacuum in chamber 228 is maintained.

Alternately, material may be fed to furnace 226 through the lockingchamber 235, it being understood that suitable means, not shown forconvenience of illustration is provided for conveying the materialbrought in by feed means 236 to the furnace 226. Looking means 237 'isprovided for restoring the seal to the vacuum chamber after the feedingof material is complete,

The aforementioned pouring ladle is shown in dashed outline at 231within the vacuum enclosure; it moves through the lock 240 to a lowerportion 241 of passageway forming means 242 once the ladle 231 at leastpartially filled with purified molten material, and is thence removed.

It will be understood that means, not shown for convenience ofillustration, is provided for forming an electrical connection to thefurnace 226 symbolized by lead 246, the electrical connection to theelectrode 232 being symbolized by lead 247, these being connected toterminals of opposite polarity of a source of potential for producing anare from the electrode 232 to the melt in furnace 226 which has at leastsome electrically conductive characteristic.

Particular reference is made now to FIG. 12, illustrating the effect ofthe magnetic field 251 set up by the'field coil 252 within the electrode253 has in stirring the melt 254. The are current path is illustrated at255. The stirring of the melt by the magnetic field produces a morehomogeneous melt, assists in bringing to the surface impurities whichmay be vaporized as a result of the vacuum atmosphere, and wherematerials are mixed to form an alloy, the stirring of the melt assistsin the distribution of materials to form an alloy of uniformconstruction.

Mold 123, FIG. 7, and mold 222, FIG. 10, may have movable bottomscorresponding to bottom 159, FIG. 8, so that continuous casting may bedone with these electrode configurations.

By way of further summary of the processes of my invention which may bepracticed by certain embodiments of apparatus heretofore described whichare suitable therefor, but which processes may be practiced by othersuitable apparatus, with particular reference to FIG. 2 the process ofmy invention includes the steps of transferring successive portions of amolten metal to be purified to a vacuum chamber, utilizing an electricarc to add heat to the portion of the metal in the vacuum chamber tomaintain said portion at a desired temperature, the vacuum chamber beingevacuated to a pressure at which the impurities are vaporized, andremoving the vaporized impurities from the vacuum vessel. The inventionfurther includes the process of utilizing at least one nonconsumableelectrode disposed in the vacuum chamber for forming the electric are,no substantial vaporization of material from the electrode arcingsurface which produces the electric arc occurring. The process furtherincludes the step of forming an electric arc to the molten material inthe vacuum chamber. The process further includes the use of directcurrent to produce the arc, in which the nonconsumable electrode isconnected in the electric circuit to form the anode. The process furtherincludes the additional step of adjusting the position of thenonconsumable electrode with respect to the molten material in thevacuum chamber as the level of the molten material changes therein. Theprocess further includes using two coaxially disposed nonconsumableelectrodes each producing an arc to the molten material in the vacuumchamber to supply heat thereto, or producing one are between each other.The process further includes three coaxial electrodes connected to athree-phase source and producing three arcs to the molten material inthe vacuum chamber, and also the use of three nonconsumable electrodeswhich may be disposed in a triangular pattern connected to a three-phasesource for producing three arcs to the molten material in the vacuumchamber to supply heat thereto and control the tem-.

perature of the molten material in the vacuum chamber to therebymaintain at a temperature most conducive to the removal of impuritiestherefrom having vapor pressures greater than the pressure to which thevacuum chamber has been evacuated.

My invention further includes producing a vacuum in the vacuum chamberlimited only by the pressure at which substantial evaporation ofmaterial from the arcing surface or surfaces producing the arc occurs.

ill

The aforedescribed process includes the step of mixing the degassedmetal with the balance of metal which has a higher gas content. Theprocess also includes the step of utilizing the pressure of theatmosphere to force molten metal into the vacuum vessel.

A process of my invention which may be practiced by the apparatus ofFIG. 7 and by other apparatus includes feeding particulate material intoan evacuated mold, utilizing a non consumable electrode with afluid-cooled arcing surface to produce an arc to heat the material andform a molten pool, the nonconsumable electrode having field coil meanstherein to substantially continuously move the arc and stir the materialin the molten pool, and gradually withdrawing the electrode as a solidingot forms under the molten pool, impurities in the material in theparticulate charge vaporizing at the low pressure in the evacuated moldand being removed therefrom by vacuum suction. The process includes thefurther step of feeding the particulate charge around the outsidediameter of the electrode. The process further includes the step offeeding charge to the molten pool through a central axial aperturepassing through the electrode. The process further includes the step offeeding additional material into the evacuated mold along the insidewall thereof. The process also includes utilizing two concentricnonconsumable electrodes having an arc therebetween near the molten poolto supply heat to the molten pool and feeding particulate charge throughthe space between electrodes.

The process also includes the use of two nonconsumable electrodespassing through the sidewalls of the evacuated mold, at least one ofsaid electrodes having a central passageway therethrough, and feedingmaterial through said central passageway to the molten pool. The processalso includes in combination with additional steps heretofore related,the use of a field coil around the outside of a mold composed ofnonmagnetic material for stirring the molten material of the pool.

A continuous casting process of my invention may be practiced by theapparatus shown in FIG. 8 and includes the steps of forming an arebetween a pair of nonconsumable electrodes in an evacuated mold, themold having a retractable base portion, feeding particulate charge intothe mold to first form a pool of molten metal on the base portion,vaporized impurities being removed from the molten pool by vacuumaction, and thereafter retracting the movable base portion as a hardenedingot forms in the mold, the rate of retraction being coordinated withthe rate of charge material feed and the growth of the hardened portionof the ingot to maintain the level of the molten pool at a desired levelwith respect to the arc supplying heat thereto. The molds of FIGS. 7 and10, for example, may have retractable base portions to permit continuouscasting.

A process of my invention which may be practiced with the apparatusshown in FIG. 12 is to utilize a nonconsumable electrode having a fieldcoil therein near the arcing surface to produce an arc to a melt, andenergizing the field coil to substantially continuously rotate the arearound the arcing surface, the rotation of the are causing stirring ofthe melt and resulting in a more homogeneous melt.

A process according to my invention which may be practiced utilizing theapparatus of FIG. 11 and other apparatus includcs producing a moltenpool of metal in a skull furnace enclosed within the vacuum chamber byproducing an electric arc to the material while feeding charge to thefurnace and thereafter pouring an ingot ofthe molten material from whichimpurities having a vapor pressure higher than the pressure within thevacuum chamber have been removed, and thereafter removing the ingot fromthe vacuum chamber. A further step in the above-described processincludes utilizing a substantially nonconsumable electrode to heat thematerial without substantial contamination. A further step includesevacuating the chamber to a pressure level the limit of which is setonly by evaporation of material from an arcing surface of a fluid-cooledarc-rotating nonconsumable electrode. A further step includes utilizinga nonconsumable electrode with a passageway therethrough for feedingcharge to the furnace.

derstood that the drawings and the writtendescriptionare ex emplary andillustrative only and should not be interpretediin a limiting sense.

Iclaim:

1. Apparatus for forming an ingot while at the same time. removingimpurities from the metal forming the ingot comprising, in combination,an at least partially evacuated mold,,

at least one nonconsumable electrode extending into said. mold andelectrically insulated therefrom, the nonconsumablevv electrodeincluding means forming a fluid-cooled arcing surface and a field coildisposed therein near the arcing surface for substantially continuouslymoving the arc over the arcing surface, and means for supplying a chargeto the mold while. maintaining the vacuum therein, the arc fromtheelectrodei producing from the charge a pool of molten metal whichhardensand becomes relatively cool at the bottom thereof distant from the arcto form an ingot, impurities in the metal of the charge having a vaporpressure greater than the pressure within the mold at substantially thetemperature of the molten pool being removed from the vacuum chamber; I

2. Apparatus according to claim 1 including inaddition a sleeve ofrefractory material extending around the outside wall of thenonconsumable electrode and spaced therefrom to form a cylindricalpassageway, in which the charge is particulate, and in which the meansfor feeding the particulate-chargeinto the mold includes means forfeeding the charge through said cylindrical passageway.

3. Apparatus according to claim 1 in which the nonconsumable electrodeis additionally characterized as having an axial passageway extendingtherethrough and in which means for feeding a particulate charge intothe mold includes said axial passageway.

4. Apparatus according to claim 2 including other additional means forfeeding a particulate charge into the mold through a plurality ofpassageways thereinto.

5. Apparatus according to claim I in which the mold is furthercharacterized as having aremovable base, the cooled ingot aftershrinking being removable through the opening formed by removing thebase.

6. Apparatus according to claim 1 including second nonconsumableelectrode extending into said mold, the first? named and secondnonconsumable electrodes being mounted' coaxially with respect to eachother and spaced from the electrically insulated from each other, eachof the nonconsumable electrodes including means forming a fluid-cooledannular arcing surface and a field coil for setting up a magnetic fieldto cause the arc therefrom to rotate substantially continuously in anannular path around the annular arcing surface, the first named andsecond electrodes being adapted to be connected to terminals of oppositepolarity of a source of potential to, produce and sustain an arctherebetween.

7. Apparatus according to claim 6 in which the electrode of smallerdiameter of the two nonconsumable electrodes is further characterized ashaving an axially extending passageway therethrough, and including inaddition vacuum pump means operatively connected to said passagewaywhereby the interior of the mold is evacuated by way of said passageway.

8. Apparatus according to claim 6 in which particulate; charge is fedinto the mold through the cylindrical space. between the first andsecond electrodes.

9. Apparatus for continuous casting of an ingot while removingimpurities from the material whichis to form they ingot comprising, incombination, a hermetically sealable mold having a retractable bottom,retracting means connected to said retractable bottom, vacuum pump meansoperatively connected to the interior of the mold for producing andsustaining at least a partial vacuum therein while sealed, at least onenonconsumable electrode extending into the mold and electricallyinsulated therefrom, the nonconsumable electrode having means forming afluid-cooled arcing surface and a field coil therein near the arcingsurface for setting up a magnetic field to substantially continuouslymove an arc therefrom over said arcing surface, the electrode beingadapted to be electrically connected to a source of potential to producesaid are within the mold, means for feeding a charge of material bemelted into the mold while maintaining the vacuum therein, said arereducing said material to a molten state and forming of the melt amolten pool, a relatively cool and hardened ingot forming beneath saidpool, said ingot increasing in length as additional charge is added intothe mold, said retractable bottom being adapted to be lowered by saidretracting means as the cooled and hardened ingot lengthens to maintainthe position of the molten pool within the mold substantially constant,the material feed and the ingot move- 14 ment being adapted to becoordinated to provide for continuous casting, said mold being adaptedto have a portion of the hardened ingot removed therefrom withoutinterrupting the feeding of charge material into the mold orinterrupting the arc produced therein.

10. Apparatus according to claim 9 in which the melt constitutes asurface of opposite polarity and the arc takes place between theelectrode and the melt.

11. Apparatus according to claim 9 in which the electrode isadditionally characterized as having an axial passageway therethrough,and the charge material is fed into the mold through said axialpassageway.

12. Apparatus according to claim 9 including in addition a secondnonconsumableelectrode similar to the first named electrode extendinginto the mold, and in which the arc takes place between electrodes.

13. Apparatus according to claim 12 in which both said nonconsumableelectrodes have axial passageways therethrough for feeding a charge tothe molten pool within the mold.

